1. Field of the Invention
The present invention relates to a method for the manufacture of a stabilized filament superconductor wherein rods each having a core of superconductor material are bundled together and are surrounded with a jacket of stabilization material having good electrical conductivity. The composite member thus produced is subjected to a cross section reducing deformation by means of extrusion and/or drawing.
2. Description of the Prior Art
A method of the type with which the present invention is concerned is disclosed, for example, by Swiss Pat. No. 456 790, which corresponds to German OS No. 1 640 506. In the method disclosed therein, hexagonal rods of copper which contain a core of superconductive material such as, for example, NbTi are bundled together and are surrounded by a tubular copper jacket. The entire assembly is closed and subjected to a cross section reducing deformation by extrusion, drawing, or some other type of deformation until a superconductive wire having the desired outside diameter is obtained.
In medical technology, particularly nuclear magnetic resonance tomography, superconductive magnets are required in which the proportion of stabilization material far exceeds the cross-sectional area of the cores of superconductive material. If such a superconductor were to be manufactured in the manner previously set forth, then an extrusion bar having a relatively low proportion of superconductive cross section would have to be prepared and then would have to be subsequently deformed by means of expensive extrusion and subsequent drawing processes. With respect to the superconductive cross section of the finished conductor, significantly higher manufacturing costs are thus necessitated in comparison to conductors which have a lower proportion of stabilization material.
In the manufacture of conductors having a ratio of stabilization material to superconductor material between 10:1 and 15:1, a filament superconductor having a relatively low proportion of stabilization material has first been manufactured, deformed, and then provided with additional stabilization material. German Pat. No. 30 45 277, for example, discloses such an arrangement. That patent discloses a composite member which contains superconductive wires and is soldered into the channel of a stabilizing metal profile. In this way, the relatively expensive extrusion process for the composite member including superconductive material is applied to only a part of the overall cross section and significantly lower manufacturing costs are achieved in comparison to the previously described method. It is not possible, however, to provide other than a rectangular superconductor having filaments asymmetrically arranged therein. Further, it is not possible to significantly heat the finished superconductor so that using insulation with a lacquer which hardens under the influence of heat is not possible. Other insulators must therefore be employed and these insulators are not only expensive, but also reduce the packing density of the wound superconductor in the finished magnet.